1. Technical Field
This disclosure relates generally to electronic circuits, and more particularly to a circuit and method for generating a clock signal, as well as a real time clock device comprising the circuit for generating a clock signal.
2. Description of the Related Art
A crystal oscillator is an electronic circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency. This frequency is commonly used to keep track of time (as in quartz wristwatches), to provide a stable clock signal for digital integrated circuits, and to stabilize frequencies for radio transmitters and receivers. The most common type of piezoelectric resonator is the quartz crystal, so oscillator circuits designed based on them are called “crystal oscillators”.
Quartz oscillators provide an accuracy far superior to that of other conventional oscillator designs, but they are not perfect. Quartz crystals are sensitive to temperature variations, and may lead to degraded accuracy of the time information or clock signal in systems which, for example, may include a real time clock (RTC), a communication terminal and so on.
One approach that has been used to compensate for the time or signal error is adjusting the frequency at which the crystal oscillator oscillates by adding additional capacitive load across a crystal. Another approach that has been used is periodically modifying the frequency by deleting or inserting clock pulses. And an accuracy of better than 3-5 ppm can be obtained.